I've been reading about the LANMAN (LM) hash and I'm curious about a particular part of the algorithm.
The LM hash is computed as follows:
- The user’s ASCII password is converted to uppercase.
- This password is null-padded to 14 bytes.
- The 14-byte password is split into two 7-byte halves.
- These values are used to create two DES keys, one from each 7-byte half.
- Each of the two keys is used to DES-encrypt the constant ASCII string "KGS!@#$%", resulting in two 8-byte cipher-text values.
- These two cipher-text values are concatenated to form a 16-byte value, which is the LM hash.
There are a lot of security weaknesses outlined in the linked Wikipedia article and talked about elsewhere, but I'm particularly interested in steps 3 through 6. I'm curious about what led to this design. Is there any real security advantage to splitting a password, encrypting the two halves separately, then combining the two halves to form one hash again? Or is this just an example of "security through obscurity"?